Assessment of four strain energy decomposition methods for phase field fracture models using quasi-static and dynamic benchmark cases

Strain energy decomposition methods in phase field fracture models separate strain energy that contributes to fracture from that which does not. However, various decomposition methods have been proposed in the literature, and it can be difficult to determine an appropriate method for a given problem. The goal of this work is to facilitate the choice of strain decomposition method by assessing the performance of three existing methods (spectral decomposition of the stress or the strain and deviatoric decomposition of the strain) and one new method (deviatoric decomposition of the stress) with several benchmark problems. In each benchmark problem, we compare the performance of the four methods using both qualitative and quantitative metrics. In the first benchmark, we compare the predicted mechanical behavior of cracked material. We then use four quasi-static benchmark cases: a single edge notched tension test, a single edge notched shear test, a three-point bending test, and a L-shaped panel test. Finally, we use two dynamic benchmark cases: a dynamic tensile fracture test and a dynamic shear fracture test. All four methods perform well in tension, the two spectral methods perform better in compression and with mixed mode (though the stress spectral method performs the best), and all the methods show minor issues in at least one of the shear cases. In general, whether the strain or the stress is decomposed does not have a significant impact on the predicted behavior.

SSOP Three-Dimensional Reconstruction of Tibia and Fibula for Applications in Biomechanical Fracture Models

Context: Non-fatal injuries represent a public health issue. Among them, lower limb fractures have a large impact on the costs related to orthopedic treatments. In this work, a three-dimensional reconstruction of the tibia and fibula was performed for biomechanical applications with the purpose of defining the 3D reconstruction parameters that allow reducing patients’ radiation exposure and computational costs. Method: For the 3D reconstruction, a computerized tomography taken from a volunteer was used, as well as two software applications specialized in DICOM image reconstruction (Mimics Research and 3DSlicer). The number of images included in the volume was modified, and the results were compared. The quality of the reconstructed volumes was verified by comparing the reference volume reconstructed with the total number of images/slices vs. the modified volumes. The MeshLab software was used for this purpose. The analyzed parameters were the distance differences between the reference and the alternative models, as well as the qualitative curvature analysis. Results: The ANOVA results for the Max (maximum distance between meshes) response shows that software and slices are significant factors. However, the software-slices interaction did not have a significant influence. As for the RMS (root mean square) distance response, software, slices, and the software-slices interaction are not significant. For the Mean distance response, slices and the software-slices interaction are not significant. Nevertheless, software significantly influences the response. These results suggest a potential way to reduce the computational cost and the patient’s radiation exposure in future biomechanical and preoperatory analyses, since the same quality can be obtained by including fewer 2D images in the reconstruction. Conclusions: The reconstructed surfaces are smoother when Mimics is used, even though the same smoothness factor was employed in both software applications during the reconstruction. When 16 slices are used (retained every 16 images from the complete original model), the distance differences increased for both bones (tibia and fibula). For the RMS, reducing the number of slices and using either one of the two applications analyzed would not show any significant differences in the reconstruction, thus allowing the potential reduction of radiation exposure of the patient. Acknowledgements: The authors are grateful to Universidad Nacional de Colombia for funding the project “Estado de esfuerzos en un elemento de osteosíntesis en la consolidación de una fractura de miembro inferior”.

Iteratively Coupled Flow and Geomechanics in Fractured Poroelastic Reservoirs: A Phase Field Fracture Model

Fluid-solid coupling in fractured reservoirs plays a critical role for optimizing and managing in energy and geophysical engineering. Computational difficulties associated with sharp fracture models motivate phase field fracture modeling. However, for geomechanical problems, the fully coupled hydromechanical modeling with the phase field framework is still under development. In this work, we propose a fluid-solid fully coupled model, in which discrete fractures are regularized by the phase field. Specifically, this model takes into account the complex coupled interaction of Darcy-Biot-type fluid flow in poroelastic media, Reynolds lubrication governing flow inside fractures, mass exchange between fractures and matrix, and the subsequent geomechanical response of the solid. An iterative coupling method is developed to solve this multifield problem efficiently. We present numerical studies that demonstrate the performance of our model.

What Is Really Happening When Parent and Child Wells Interact?

When trying to understand the well-to-well events known as frac hits and fracture-driven interactions (FDIs), the first idea to embrace is this: they are not all the same. “And the key physical mechanisms are not the same,” said Mark McClure, who added that, “Until you’ve really dialed in on what those are, you’re really in the dark.” McClure is the cofounder and CEO of ResFrac Corp. In March, the modeling firm began a multiclient study to diagnose the relationships between parent and child wells—or what many consider to be the ultimate subsurface challenge facing the shale sector. Participating operators are Marathon Oil, Hess Corp., Pioneer Resources, Arc Resources, Birchcliff Energy, SM Energy, and Ovintiv Inc. These independent E&Ps represent a cross section of some of the most active plays in North America: the Midland and Delaware basins and the Bakken and Montney shales. But what makes the study unique, McClure said, is that it involves 10 rich data sets from well pads that were subjected to a number of cross-validating diagnostics: tracers, pressure/interference monitoring, geochemistry, and fiber optics. ResFrac has been using that data to calibrate its coupled reservoir-fracture models to see what knobs clients might want to turn in the future to improve well economics. The study is also trying to unearth some firm answers about what is really happening during offset stimulations, why it is happening, and what can be done to mitigate negative outcomes. ResFrac and its clients expect to wrap up this part of the study by the year’s end and to submit an abstract for an SPE technical conference in 2022. As the study nears an end, McClure offered some of his key observations that he noted are supported by previous research found within industry literature. So, What’s the Worst That Can Happen? A growing chorus of subsurface experts consider unwanted chemical reactions in the fracture network as one of the major damage mechanisms resulting from FDIs. McClure is not only among them, he said chemical effects represent the “worst” that can happen when parents and children interact. “This is where you see wells get hit, they lose 80% of their production, and it doesn’t come back,” he explained. Some in the industry have taken to calling the byproduct of these chemical reactions “shmoo” or “gunk.” For answers as to why this is happening, McClure points to two technical papers in particular.

A Similarity Solution for Imbibition Process and its Adaptation in Finite Difference Simulation of Fractured Reservoirs

The imbibition process due to capillary force is an important mechanism that controls fluid flow between the two domains, matrix and fracture, in naturally or hydraulically fractured reservoirs. Many simulation studies have been done in the past decades to understand the multi-phase flow in the tight and shale formation. Although significant advances have been made in large-scale modeling for both unconventional and conventional fields, the imbibition processes in the fractured reservoirs remains underestimated in numerical simulation, that limits confidence in long-term field production predictions. In the meanwhile, to simulate the near-fracture imbibition process, traditionally very-fine simulation grids have to be applied so that the physical phenomena of small-length scale could be captured. However, this leads to expensive computation cost to simulate full-field models with a large number of fractures. To improve numerical efficiency in field-scale modeling, we propose a similarity solution for the imbibition process that can be incorporated into the traditional finite difference formulation with coarse grid cells. The semi-analytical similarity solutions are validated by comparing with numerical simulation results with fine-scale grids. The comparison clearly indicates that the proposed algorithm accurately represents the flow behaviors in complex fracture models. Furthermore, we adopt the semi-analytical study to hydraulic fracture models using Embedded Discrete Fracture Model (Lee et al., 2001) in our numerical studies at different scales to represent hydraulic fractures that are interconnected. We demonstrate: 1) the imbibition is critical in determining flow behavior in a capillary force dominant model, 2) conventional EDFM has its limitation in capturing sub-cell flow behaviors near fractures, 3) combining the proposed similarity solution and EDFM, we can accurately represent the multi-phase flow near fractures with coarser grids, and 4) it is straightforward to adapt the similarity solution concept in finite-difference simulations for fractured reservoirs

Integrated Geomechanical Modeling and Hydraulic Fracturing Design: From Particular Cases to the Overall Result

Objective and scope The objective of the work is to present an adequate workflow for conditioning geomechanical data and hydraulic fracturing design, adjustment and simultaneous verification of a MEM and hydraulic fracture models. These approaches are relevant for greenfields and also can be used when changing field development systems: from vertical fracked wells to a system of horizontal wells with multistage fracs. Methods, techniques, and process description The paper provides examples of issues in hydraulic fracturing planning due to poor attention to the reliability and robustness of geomechanical data. Given the critically of data quality, the authors describe a holistic approach used in collecting, analysing and conditioning data for building a MEM (1D; if necessary, 3D) as the basis of a frac design. Mini-frac is considered not only as a tool for setting the hydraulic fracturing design parameters, but also as a source of data for cross-calibration between the MEM and the hydraulic fracture models. Case studies of various HF models will demonstrate the influence of MEM-and-frac uncertainties and the tools for considering them in practical HF modelling. An approach to systematic clustering of input data for HF designs is described. The importance of measuring the fracture heights is stressed as a source of data for cross-calibration of HF and GM models. Results and conclusions The correct sequence of work, data consolidation and successive data refinement helps to maintain the database of elastic and strength properties of various target reservoirs, which proves the demand for core analysis and well logging, as well as geomechanical modelling. The improved quality of HF designs leads to better reliability of forecasts and proposed field development and individual wellwork strategies. The close integration of GM studies and modelling with HF design building enhances the operation culture, accelerates and streamlines the HF model build and validation processes, which can be a pace-setting experience for other oil and gas industries that are GM data users. Novelty and achievements The TNNC and RN-CEPiTR teams work in close cooperation and provide GM and HF integration to assess the fracture height in the target reservoirs at the Company's assets in order to improve the quality of HF modelling. The uncertainty influence on the HF design is reducing, so as the risks of screen-out and the risks of breakthrough into undesirable zones. The approach streamlines the engineering support for the hydraulic fracturing activity and understanding of the fracture parameters as the operations move from single-stage hydraulic fracturing to the optimized field development using horizontal wells with multi-stage hydraulic fracturing.